MINNEAPOLIS, MN – May 6, 2014 – For over 30 years, aspirin has been known to prevent heart attacks and strokes, but who exactly should take a daily aspirin remains unclear. New research published today in Circulation: Cardiovascular Quality and Outcomes shows that your coronary artery calcium (CAC) score, a measurement of plaque in the arteries that feed the heart, may help determine whether or not you are a good candidate for aspirin.

"Many heart attacks and strokes occur in individuals who do not appear to be at high risk," states lead author, Michael D Miedema, MD, MPH. "Individuals with known CVD [cardiovascular disease] should take a daily aspirin, but the best approach for individuals without known CVD is unclear. If we only treat high-risk individuals with aspirin, we are going to miss a substantial portion of patients who eventually suffer heart attacks. However, liberally prescribing aspirin increases the bleeding risk for a significant number of people who were never going to have a heart attack in the first place. With this study, we wanted to see if there is potentially a better way to determine who to treat with aspirin beyond simply using traditional risk factors."

Aspirin helps prevent heart attacks and strokes by preventing blood clots from forming in arteries lined with unhealthy plaque buildup. However, this same benefit puts patients taking aspirin at risk for dangerous bleeding, when blood clots don't form where they should. For that reason, the American Heart Association (AHA) guidelines currently recommend aspirin to prevent cardiovascular disease (CVD) in people who have known CVD or who are considered to be at high risk for a CVD event. Aspirin is generally not recommended for people who are considered to be at low or intermediate risk.

In this retrospective study, researchers studied 4,229 participants in the Multi-Ethnic Study of Atherosclerosis (MESA) from six centers across the country. Participants included had no known CVD or diabetes, were not on aspirin therapy, and were followed for approximately 7 years.

Participants were grouped according to their CAC score and the rates of heart attacks in each group were calculated. Based on these rates, the research team weighed the likelihood of an individual to benefit from aspirin therapy (the potential of the aspirin to prevent a heart attack) against the likelihood of harm (the potential for the aspirin to cause major bleeding). They estimated that participants with elevated CAC scores (>100) were 2−4 times more likely to benefit from aspirin therapy than to be harmed, even if they did not qualify for aspirin use according to current AHA guidelines. Conversely, MESA participants with no calcified plaque (CAC score = 0) were 2−4 times more likely to be harmed by aspirin use than to benefit. The results in both groups held true even after accounting for traditional risk factors.

"We estimate that individuals with significant plaque buildup in the arteries of the heart are much more likely to prevent a heart attack with aspirin use than to suffer a significant bleed" explains Miedema. "On the opposite end of the spectrum, if you don't have any calcified plaque, our estimations indicate that use of aspirin would result in more harm than good, even if you have risk factors for heart disease such as high cholesterol or a family history of the disease."

Miedema added, "A CAC score of zero is associated with a very low risk of having a heart attack. That means individuals with a score of zero may not benefit from preventive medications, such as aspirin as well as the cholesterol-lowering statin medications. Approximately 50% of middle-aged men and women have a CAC score of zero, so there is a potential for this test to personalize the approach to prevention and allow a significant number of patients to avoid preventive medications, but we need further research to verify that routine use of this test is the best option for our patients."